Patch up an Event of differences (like those produced by
Event.diff) into an Event that reflects the current
version of a data structure.

Patch up an Event of differences (like those produced by
Event.diff) into an Event that reflects the current
version of a data structure. That is: (event:
Event[CC[T]]).diff.patch is equivalent to event

Build a new Event representing a sliding window of at-most n.
Each event notified by the parent are added to a queue of size
at-most n. This queue is in turn notified to register of
the returned event.